SOFC (Solid Oxide Fuel Cell) power generation system with carbon dioxide trapping function and operation method of SOFC power generation system
By combining the anode support and electrolyte support SOFC stack module and heating resistance, the fuel is completely converted into water vapor and CO2, which solves the problem of CO2 capture and water supply dependence in the SOFC power generation system, and achieves high-purity CO2 capture and system simplification.
Patent Information
- Application Number
- CN202510598186.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-09
- Publication Date
- 2025-09-05
AI Technical Summary
The existing SOFC power generation system has difficulties in CO2 capture and water supply dependence. The CO2 capture cost is high and the system is complex, and the dependence on external equipment on water vapor supply leads to increased system burden and cost.
The anode support and electrolyte support SOFC stack module are combined with heating resistance to achieve complete consumption of water vapor and CO2. High-purity CO2 is recovered through heat exchange and condensation, and the condensed water vapor is reused for the reforming reaction to get rid of the dependence on external water supply.
It realizes low-cost capture of high-purity CO2, reducing system complexity and cost, and at the same time, it gets rid of the dependence on external water supply under the rated power generation state.
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Figure CN120600870A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of fuel cell systems, and in particular to a SOFC power generation system with a carbon dioxide capture function and an operating method thereof. Background Art
[0002] Solid Oxide Fuel Cell (SOFC) is the most efficient power generation technology among all power generation equipment. The power generation efficiency of a single unit can reach more than 60%, and it has a wide range of fuel sources and low pollutant emissions. It is a clean, low-carbon, safe and efficient power generation method. It has broad application prospects in the field of distributed power supply for civil and commercial users such as residences, hotels, hospitals, schools, office buildings, communities, data centers, and communication base stations. Therefore, it is considered to be a new energy power generation technology with the broadest development and application prospects in the future.
[0003] The conventional high-power SOFC power generation system currently under development uses natural gas as fuel. The natural gas is heated, reformed, and then enters the SOFC stack module for electrochemical reaction to generate electricity. The anode-supported SOFC stack module has lower resistance and higher power generation efficiency, but the stack has poor robustness and excessive fuel utilization will damage the stack. The unreacted fuel in the SOFC stack enters the burner and mixes with air to burn, generating high-temperature flue gas to maintain the thermal balance of the system. The CO2 generated by natural gas in a series of electrochemical reactions and combustion processes accounts for a small proportion in the large flow of high-temperature flue gas, which makes it very difficult to capture CO2 at low cost.
[0004] In addition, the SOFC power generation system requires a certain flow of water vapor during operation for the reforming reaction of natural gas in the reformer and SOFC stack module. Once the water vapor supply is cut off or the flow is insufficient, the SOFC stack module will inevitably be damaged. If the SOFC power generation system wants to get rid of its dependence on external water supply, it can adopt a high-temperature anode tail gas recirculation process to circulate the high-temperature water vapor-containing anode tail gas at the stack module outlet to the reformer inlet and mix it with fresh natural gas before re-entering the system. However, the high-temperature anode tail gas circulation fan is technically difficult, costly, has a limited service life and complex system control. If the flue gas condensate water recovery method is adopted, the large flow of flue gas at the burner outlet needs to be condensed, and the condensing device occupies a large area and is costly.
[0005] Therefore, there is an urgent need for a new type of SOFC power generation system that can achieve low-cost recovery of high-purity CO2, reduce system cost and complexity, and get rid of dependence on external water supply. Summary of the Invention
[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.
[0007] The embodiments of the present application provide a SOFC power generation system with carbon dioxide capture function and its operation method. By maintaining the thermal balance of the system, the purity of the captured CO2 can be effectively improved. At the same time, water vapor is reused for the reforming reaction, which can get rid of the dependence on external water supply during rated power generation.
[0008] This application provides the following technical solutions:
[0009] In the first aspect, an embodiment of the present application provides a SOFC power generation system with a carbon dioxide capture function, comprising: an anode-supported SOFC stack module, an electrolyte-supported SOFC stack module, a heating resistor, a start-up burner, a steam generator, a reformer, a fuel preheater, a fan, an air preheater, a condenser, a water pump, a first stop valve, a second stop valve, a third stop valve and a fourth stop valve, wherein the anode-supported SOFC stack module, the electrolyte-supported SOFC stack module and the heating resistor cooperate with each other to consume the fuel in the system to generate water vapor and CO2, and the water vapor is used for the reforming reaction of the SOFC system.
[0010] In combination with the first aspect, in one embodiment of the present application, the rated power generation operating temperature range of the anode-supported SOFC stack module is 650°C to 750°C, and the rated power generation operating temperature range of the electrolyte-supported SOFC stack module is 750°C to 850°C.
[0011] In combination with the first aspect, in one embodiment of the present application, the anode outlet of the anode-supported SOFC stack module is connected to the anode fuel inlet of the electrolyte-supported SOFC stack module, the cathode outlet of the anode-supported SOFC stack module is connected to the cathode air inlet of the electrolyte-supported SOFC stack module, the connectors between the fuel pipes and air pipes of the anode-supported SOFC stack module and the electrolyte-supported SOFC stack module are both made of ceramic metal parts, and the current generated by the anode-supported SOFC stack module enters the inverter of the SOFC power generation system through a wire.
[0012] In combination with the first aspect, in one embodiment of the present application, the two ends of the electrode of the electrolyte-supported SOFC stack module are connected through the heating resistor, and the heating resistor is used to convert current into thermal energy. The current is generated by the electrochemical reaction of the fuel exhaust gas and air exhaust gas of the anode-supported SOFC stack module entering the electrolyte-supported SOFC stack module.
[0013] In combination with the first aspect, in one embodiment of the present application, an ignition device is provided in the starting burner, and the ignition device is used to activate the starting burner. The starting burner burns the fuel and air introduced into the SOFC power generation system to make the temperature of the electrolyte supporting the SOFC stack module reach 750°C to 850°C.
[0014] In combination with the first aspect, in one embodiment of the present application, the first stop valve is arranged on the connecting pipeline between the anode outlet of the electrolyte-supported SOFC stack module and the high-temperature side inlet of the steam generator, the second stop valve is arranged on the pipeline between the fuel inlet of the startup burner and the rear-end pipeline tee of the anode outlet of the electrolyte-supported SOFC stack module, the third stop valve is arranged on the pipeline between the high-temperature flue gas outlet of the startup burner and the inlet pipeline tee of the steam generator, and the fourth stop valve is arranged on the pipeline between the external H2O pipeline and the water pump inlet pipeline tee.
[0015] In a second aspect, an embodiment of the present application provides an operating method for a SOFC power generation system with a carbon dioxide capture function, which is applied to the aforementioned SOFC power generation system with a carbon dioxide capture function, and the method comprises the following contents: (1) opening a first stop valve and a third stop valve of the SOFC power generation system, closing a second stop valve and a fourth stop valve, turning on a blower of the system, and introducing natural gas into the system; when air and the natural gas enter a start-up burner of the system, starting an ignition device of the start-up burner to activate the start-up burner to burn the natural gas; (2) when the temperatures of the reformer, the anode-supported SOFC stack module, and the electrolyte-supported SOFC stack module of the system all exceed 300°C, keeping the first stop valve and the third stop valve open, opening the fourth stop valve, and pumping water into the steam generator through the water pump; Deionized water is supplied, and the high-temperature steam generated by the steam generator is mixed with the natural gas and then enters the reformer and the SOFC stack module; (3) when the temperature of the anode-supported SOFC stack module reaches 650°C to 750°C, the flow rate of the natural gas is adjusted, and the anode-supported SOFC stack module draws the load current; (4) when the anode-supported SOFC stack module reaches full-load power generation conditions and the outlet temperature of the electrolyte-supported SOFC stack module reaches 750°C to 850°C, the electrolyte-supported SOFC stack module draws the load current, and when the fuel utilization rate of the electrolyte-supported SOFC stack module reaches 100%, the second stop valve is opened, and the first stop valve, the third stop valve and the fourth stop valve are closed; (5) the flow rate of the circulating coolant is adjusted to separate high-purity CO2 from the condenser.
[0016] Compared with the existing technology, the advantages of this application are: it utilizes the characteristics of the electrolyte-supported SOFC stack module, which has high power generation operating temperature, high fuel utilization rate, and complete isolation of fuel and air, and cooperates with the heating resistor to directly convert the electricity generated by the electrolyte-supported SOFC stack module into heat to maintain the thermal balance of the system; the fuel in the system is completely consumed and only water vapor and CO2 are produced, which are isolated from the air. The exhaust gas generated by the fuel is completely captured through heat exchange, waste heat recovery, and water vapor condensation to achieve complete capture of high-purity CO2; in addition, the condensed water vapor re-enters the SOFC system for reforming reaction, so that the SOFC system is free from dependence on external water supply under rated power generation state. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.
[0018] Figure 1 A process flow chart of a SOFC power generation system with carbon dioxide capture function provided by one embodiment of the present application;
[0019] Figure numerals: anode-supported SOFC stack module 1; electrolyte-supported SOFC stack module 2; heating resistor 3; starting burner 4; steam generator 5; reformer 6; fuel preheater 7; fan 8; air preheater 9; condenser 10; water pump 11; first stop valve 12; second stop valve 13; third stop valve 14; fourth stop valve 15. DETAILED DESCRIPTION
[0020] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without inventive effort are within the scope of protection of this application.
[0021] It should be noted that although a logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in an order different from that in the flowchart. The terms "first" and "second" in the specification, claims, and the above-mentioned figures are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the content disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limitations of the implementation of this application. Therefore, they have no technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed in this application without affecting the efficacy and purpose of this application. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of the implementation of this application. Changes or adjustments in their relative relationships should also be considered as the scope of the implementation of this application without substantially changing the technical content.
[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein are for the purpose of describing the embodiments of this application only and are not intended to limit this application.
[0023] In the field of fuel cell system technology, in conventional high-power SOFC power generation systems, the fuel at the outlet of the SOFC stack module fails to fully react to generate electricity. The high-temperature flue gas generated after mixing with the high-temperature air at the outlet of the SOFC stack module in the burner is used to maintain the thermal balance of the system, while avoiding the emission of combustible gases such as CO and H2. However, in this solution, the flue gas flow rate is large and the CO2 content is low after the remaining fuel at the outlet of the stack module is mixed with air and burned. The cost of capturing CO2 is very high, and the cost of condensing and recovering water vapor is also high. If the SOFC system wants to get rid of its dependence on external water supply, it must use a high-temperature anode circulation fan or condense the large flow of flue gas, which will result in high system load and cost.
[0024] In view of this, embodiments of the present application provide a SOFC power generation system with carbon dioxide capture functionality and a method for operating the SOFC power generation system. The system includes an anode-supported SOFC stack module, an electrolyte-supported SOFC stack module, a heating resistor, a start-up burner, a steam generator, a reformer, a fuel preheater, a fan, an air preheater, a condenser, a water pump, a first shut-off valve, a second shut-off valve, a third shut-off valve, and a fourth shut-off valve. The anode-supported SOFC stack module, the electrolyte-supported SOFC stack module, and the heating resistor cooperate to consume fuel in the system to produce water vapor and CO2. After condensation, the water vapor can re-enter the SOFC system for reforming reactions. During operation, the anode-supported SOFC stack module, the electrolyte-supported SOFC stack module, and the heating resistor work together to consume fuel in the system to generate water vapor and CO2. The exhaust gas generated by the fuel then undergoes heat exchange and waste heat recovery steps before entering the condenser to condense the water vapor. Through this series of processes, complete capture of high-purity CO2 is achieved. In addition, the condensed water vapor can re-enter the SOFC system to participate in the reforming reaction, allowing the SOFC system to get rid of its dependence on external water supply when generating rated power.
[0025] The specific implementation of this application will be described below with reference to the accompanying drawings:
[0026] like Figure 1As shown, the present application provides a SOFC power generation system with carbon dioxide capture function, which includes an anode-supported SOFC stack module 1, an electrolyte-supported SOFC stack module 2, a heating resistor 3, a start-up burner 4, a steam generator 5, a reformer 6, a fuel preheater 7, a fan 8, an air preheater 9, a condenser 10, a water pump 11, a first stop valve 12, a second stop valve 13, a third stop valve 14 and a fourth stop valve 15. Among them, the anode-supported SOFC stack module 1 is a modular power generation device based on solid oxide fuel cell (SOFC) technology, and its core feature is a single cell stack design using the anode as a structural support. The module achieves efficient conversion of chemical energy to electrical energy through the synergistic effect of multiple functional components. The electrolyte-supported SOFC stack module 2 is a solid oxide fuel cell stack module using electrolyte material as a structural support. The module is assembled by multiple electrolyte-supported single cells in series, parallel or mixed mode to form a power generation device with a specific voltage and power output. During the operation of the system, the fuel passes through the anode-supported SOFC stack module 1 to generate electricity, undergoes an electrochemical reaction in the electrolyte-supported SOFC stack module 2, and generates heat through the heating resistor 3, and is eventually completely consumed, producing only water vapor and CO2. In this process, water vapor and CO2 can also effectively avoid mixing with air. Furthermore, the exhaust gas generated by the fuel can achieve complete capture of high-purity CO2 after heat exchange, waste heat recovery, and water vapor condensation. In addition, the condensed water vapor can re-enter the SOFC system for reforming reaction, making the SOFC system free from dependence on external water supply under rated power generation state.
[0027] In one embodiment, the rated power generation operating temperature of the anode-supported SOFC stack module 1 is 650°C to 750°C, while the rated power generation operating temperature of the electrolyte-supported SOFC stack module 2 is between 750-850°C, and the fuel utilization rate can reach 100%.
[0028] It is understandable that the electrolyte-supported SOFC stack has a high operating temperature, which can reach 850°C, and the stack is highly robust during use, with a fuel utilization rate of 100%. In addition, when an electrochemical reaction occurs in the SOFC stack, the fuel and air are separated from each other, and the fuel is completely consumed through the electrochemical reaction. Combined with the heating resistor, the chemical energy of the fuel can be completely converted into thermal energy, and at the same time, high-temperature flue gas free of N2 and O2 is obtained, which contributes to the efficient capture of CO2.
[0029] In one embodiment, the anode outlet of the anode-supported SOFC stack module 1 is connected to the anode fuel inlet of the electrolyte-supported SOFC stack module 2. Simultaneously, the cathode outlet of the anode-supported SOFC stack module 1 is connected to the cathode air inlet of the electrolyte-supported SOFC stack module 2. During system operation, the fuel exhaust gas at the anode outlet of the anode-supported SOFC stack module 1 can directly enter the anode fuel inlet of the electrolyte-supported SOFC stack module 2, while the high-temperature air at the cathode outlet of the anode-supported SOFC stack module 1 can directly enter the cathode air inlet of the electrolyte-supported SOFC stack module 2. Furthermore, the fuel and air pipe connections between the anode-supported SOFC stack module 1 and the electrolyte-supported SOFC stack module 2 can be connected using ceramic metal parts to ensure insulation between the two and prevent short circuits. The current generated by the anode-supported SOFC stack module 1 enters the inverter of the SOFC power generation system through wires and is ultimately output externally.
[0030] In one embodiment, the two ends of the electrode of the electrolyte-supported SOFC stack module 2 are connected through a heating resistor 3. The fuel exhaust gas and air exhaust gas of the anode-supported SOFC stack module 1 enter the electrolyte-supported SOFC stack module 2, and the electrochemical reaction is completely exhausted. The generated current is converted into heat energy through the heating resistor 3 to maintain the thermal balance of the system.
[0031] In one embodiment, the start-up burner 4 has a built-in ignition device that can activate the start-up burner 4. During system operation, fuel and air are introduced into the SOFC power generation system during a cold start. The high-temperature flue gas generated by the combustion of the fuel and air in the start-up burner 4 can be used to heat the system until the temperature of the electrolyte-supported SOFC stack module 2 reaches 750°C to 850°C.
[0032] In one embodiment, the first stop valve 12 is arranged on the pipeline from the anode outlet of the electrolyte-supported SOFC stack module 2 to the high-temperature side inlet of the steam generator 5, the second stop valve 13 is arranged on the pipeline between the fuel inlet of the startup burner 4 and the tee of the rear-end pipeline of the anode outlet of the electrolyte-supported SOFC stack module 2, the third stop valve 14 is arranged on the pipeline between the high-temperature flue gas outlet of the startup burner 4 and the tee of the inlet pipeline of the steam generator 5, and the fourth stop valve 15 is arranged on the pipeline between the external H2O pipeline and the tee of the inlet pipeline of the water pump 11.
[0033] In addition, the present application also provides a method for operating a SOFC power generation system with a carbon dioxide capture function. This method is applicable to the aforementioned SOFC power generation system with a carbon dioxide capture function. That is, the method can be based on the coordinated operation of various components within the system. The specific contents include:
[0034] (1) Cold start phase of the SOFC power generation system. The specific operation process includes: opening the first stop valve 12 and the third stop valve 14, and closing the second stop valve 13 and the fourth stop valve 15. Starting the blower 8, natural gas is introduced into the system, allowing air and natural gas to enter the start-up burner 4. Subsequently, the ignition device is started to activate the start-up burner 4, allowing the natural gas to be completely burned in the start-up burner 4. The heat generated is used to heat the SOFC system.
[0035] (2) SOFC power generation system temperature rise phase. The specific operation process includes: when the temperature of the reformer 6, the anode-supported SOFC stack module 1, and the electrolyte-supported SOFC stack module 2 all exceed 300°C, the first stop valve 12 and the third stop valve 14 are kept open, and then the fourth stop valve 15 is opened. Deionized water is supplied to the steam generator 5 through the water pump 11. The high-temperature water vapor generated by the steam generator 5 is mixed with natural gas and then enters the reformer 6, the anode-supported SOFC stack module 1, and the electrolyte-supported SOFC stack module 2 to prevent carbon deposits on these components.
[0036] (3) Current loading stage: The specific operation process includes: when the temperature of the anode-supported SOFC stack module 1 reaches 650°C to 750°C, the natural gas flow rate is increased, and the anode-supported SOFC stack module 1 starts to load current.
[0037] (4) Activation phase of the electrolyte-supported SOFC stack module 2. The specific operation process includes: when the anode-supported SOFC stack module 1 reaches full-load power generation and the outlet temperature of the electrolyte-supported SOFC stack module 2 reaches 750°C to 850°C, the electrolyte-supported SOFC stack module 2 begins to draw current. When the fuel utilization rate of the electrolyte-supported SOFC stack module 2 reaches 100%, the second shut-off valve 13 is opened, and the first shut-off valve 12, the third shut-off valve 14, and the fourth shut-off valve 15 are closed.
[0038] (5) Rated power generation stage: The flow rate of the circulating coolant is adjusted to separate high-purity CO2 from the condenser 10.
[0039] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.
Claims
1. A SOFC power generation system with carbon dioxide capture function, characterized in that: include: An anode-supported SOFC stack module, an electrolyte-supported SOFC stack module, a heating resistor, a start-up burner, a steam generator, a reformer, a fuel preheater, a fan, an air preheater, a condenser, a water pump, a first stop valve, a second stop valve, a third stop valve and a fourth stop valve. The anode-supported SOFC stack module, the electrolyte-supported SOFC stack module and the heating resistor cooperate with each other to consume the fuel in the system to generate water vapor and CO2, and the water vapor is used for the reforming reaction of the SOFC system.
2. The SOFC power generation system with carbon dioxide capture function according to claim 1, characterized in that: The rated power generation operating temperature range of the anode-supported SOFC stack module is 650°C to 750°C, and the rated power generation operating temperature range of the electrolyte-supported SOFC stack module is 750°C to 850°C.
3. The SOFC power generation system with carbon dioxide capture function according to claim 1, characterized in that: The anode outlet of the anode-supported SOFC stack module is connected to the anode fuel inlet of the electrolyte-supported SOFC stack module, and the cathode outlet of the anode-supported SOFC stack module is connected to the cathode air inlet of the electrolyte-supported SOFC stack module. The connectors between the fuel pipes and air pipes of the anode-supported SOFC stack module and the electrolyte-supported SOFC stack module are all made of ceramic metal parts. The current generated by the anode-supported SOFC stack module enters the inverter of the SOFC power generation system through a wire.
4. The SOFC power generation system with carbon dioxide capture function according to claim 1, characterized in that: The two ends of the electrode of the electrolyte-supported SOFC stack module are connected through the heating resistor, and the heating resistor is used to convert current into thermal energy. The current is generated by the electrochemical reaction of the fuel exhaust gas and air exhaust gas of the anode-supported SOFC stack module entering the electrolyte-supported SOFC stack module.
5. The SOFC power generation system with carbon dioxide capture function according to claim 1, characterized in that: An ignition device is provided in the starting burner, and the ignition device is used to activate the starting burner. The starting burner burns the fuel and air introduced into the SOFC power generation system so that the temperature of the electrolyte supporting the SOFC stack module reaches 750°C to 850°C.
6. The SOFC power generation system with carbon dioxide capture function according to claim 1, characterized in that: The first stop valve is arranged on the connecting pipeline between the anode outlet of the electrolyte-supported SOFC stack module and the high-temperature side inlet of the steam generator; the second stop valve is arranged on the pipeline between the fuel inlet of the startup burner and the tee of the rear-end pipeline of the anode outlet of the electrolyte-supported SOFC stack module; the third stop valve is arranged on the pipeline between the high-temperature flue gas outlet of the startup burner and the tee of the inlet pipeline of the steam generator; and the fourth stop valve is arranged on the pipeline between the external H2O pipeline and the tee of the water pump inlet pipeline.
7. A method for operating a SOFC power generation system with carbon dioxide capture function, characterized in that: The method applied to the SOFC power generation system with carbon dioxide capture function according to any one of claims 1 to 6 comprises the following contents: (1) opening a first stop valve and a third stop valve of a SOFC power generation system, closing a second stop valve and a fourth stop valve, turning on a blower of the system, and introducing natural gas into the system; after air and the natural gas enter a start-up burner of the system, starting an ignition device of the start-up burner to activate the start-up burner and burn the natural gas; (2) When the temperatures of the reformer, the anode-supported SOFC stack module, and the electrolyte-supported SOFC stack module of the system all exceed 300° C., the first stop valve and the third stop valve are kept open, the fourth stop valve is opened, and deionized water is supplied to the steam generator through the water pump. The high-temperature steam generated by the steam generator is mixed with the natural gas and then enters the reformer and the SOFC stack module; (3) When the temperature of the anode-supported SOFC stack module reaches 650° C. to 750° C., the flow rate of the natural gas is adjusted so that the anode-supported SOFC stack module draws a load current; (4) When the anode-supported SOFC stack module reaches full-load power generation, and the outlet temperature of the electrolyte-supported SOFC stack module reaches 750° C. to 850° C., the electrolyte-supported SOFC stack module draws current. When the fuel utilization rate of the electrolyte-supported SOFC stack module reaches 100%, the second stop valve is opened, and the first stop valve, the third stop valve, and the fourth stop valve are closed; (5) Adjust the flow rate of the circulating coolant to separate high-purity CO2 from the condenser.